Manholes are known for providing an opening through a structure. A cover may be provided to close the opening at a desired time. Manholes may be used in connection with containers for holding various materials. Containers are known for storing and/or transporting materials such as dry bulk material including flour, sugar, grain, fertilizer, plastic pellets, cement, and other particulate materials. Containers for storing the material include trailer tanks, rail cars, storage tanks, and the like. Access to the containers may be provided through a manhole which defines an opening into the container for such purposes as filling the container with the material, and also for providing access to the interior of the container for persons needing to view or work on the interior structures of the container. A manhole cover may be provided to close the manhole opening at the desired time such as to protect the interior of the container and its contents.
Pneumatic particulate handling systems are known for use in unloading particulate material from a container pneumatically with the use of a stream of air. Such systems are commonly used, for example, to load the material into the container of a truck trailer from another container, such as a rail car. Manhole openings may be provided to access the interior of the container for filling the container. For subsequent emptying of the container, another access opening is usually provided besides the manhole opening for which the material can exit the container pneumatically. There is a need to sealably close the manhole openings to the container to maintain an environment in the container which is at a pressure greater than atmospheric pressure during the pneumatic unloading operation.
Various concerns exist in the area of manhole covers generally and specifically in the case of providing manhole covers in pressure environments. One concern is that the manhole cover be easy to use. Another concern is that the manhole cover be safe to operate. A further often encountered concern is that the manhole cover have a low profile so as to minimize the overall height of the tank. Also, it is important that the manhole cover be easy to manufacture, and easy to maintain in an operable condition once installed. There is a need in the art for a manhole cover apparatus and method which addresses the above concerns and other concerns.